Telephone-circuit



No. 626,826. Patented June [3, [899. P. a. BURGES-S- & H. yv. w||.uEn.

TELEPHONE CIRCUIT.

(Application filed. Mar. 16, 1859.

(No Model.)

m: uonms vsrzns co.. PHOYO'LITHON wAsNms'rom n. c.

Nrrnn STATES PATENT PERCIVAL G. BURGESS, OF MEXICO, MEXICO, AND HENRY W.WILDER, OF SPRINGFIELD, MASSACHUSETTS, ASSIGNORS TO THE AMERICAN BELLTELEPHONE COMPANY, OF BOSTON, MASSACHU TTS- TELEPHONE-CIRCUIT.

SPECIFICATION forming part of Letters Patent No. 626,826, dated June 13,1899.

Application filed March 16 1 1 8 9 9.

T (LZZ whom it nuty concern:

Be it known that we,PEncIvAL G. BURGESS, residing at Mexico, Mexico, andHENRY WV. WVILDERa'esiding at Springfield, in the county of I-lampdenand State of Massachusetts, have invented certain Im prove ments inTelephone- Circuits, of which the-following is a specification.

In telephone-exchange practice conditions :0 frequently occur underwhich itbecomes desirable that of two persons engaged in conversation bytelephone one shall be able to listen to and receive messages from athird telephone, which messages or like transmitted conversation,however, shall remain unheard by the other. Such acase is found when anoperator in a telephone-exchange central station is required to attendto calls and make and supervise switch connections between substationlines and also to receive communications over an order-wire orinstruction-circuit from other operators. Sometimes also it is desirablethat the said operator shall be provided with means to so transpose theconnections of her telephones that conversation can be by themtransmitted as well as received over the latter circuit and receivedonly over the service-lines. At other times it may be desirable for thethree kinds of circuitto wit, the circuit of the operators telephone,the order-circuit, and the service-circuit of any kind-t0 be sointerconnected that each one may talk With'and hear either or both ofthe others and again for the said three circuits to be so relativelyarranged that a given one may hear and talk to the other two, which,however, cannot hear or talk with each other.

Attempts have heretofore been made to carry out the foregoing ideas moreor less perfectly, the most practical prior expedient being theemployment of such an operators receiving-telephone as that described inLetters Patent of the United States No. 487,219, granted to HammondVwHayes and Wilton L. Richards November 29, 1892, the same having twoinducing-magnets, each with its own coil and diaphragm, the poles andhelices of each magnet being arranged in a posi- Serial No. 709,357. (Nomodel.)

tion inductively neutral to that of the other;

but such a compound telephone is so heavy and cumbrous' that it cannotbe worn by an operator upon her head (except for a very short time)without inconvenience, and its efficiency is not very high. By means ofour invention the ordinary standard single-circuit telephone can be usedby the operator, and it reproduces the speech transmitted over the twoindependent circuits concernedfor example, a service-circuit and anordercircuitsubstantiallyas well as it could were it associated witheither circuit alone.

The invention comprehends a compoundcircuit arrangement wherein threetelephones are so relatively placed and connected by appropriate circuitconductors that while the receiving instrument of one of them, which wemay call A, shall be responsive to the transmission of both of theothers, B and O, and shall be able to reproduce the messages transmittedby means of the said others the receiver of B will not respond to,receive, or reproduce the transmission of G, and the reoeiver of C willin like manner be neutral or irresponsive to B. This general arrangementcan be carried into effect by connecting two of the said telephoneseither through the intermediation of repeating induction-coils ordirectly in one circuit, so that each can transmit to and receive fromthe other, and by forming a new circuit containing the third telephoneor telephone apparatus and one of the others in part from certainportions of the conductors of the first circuit and'in part of anauxiliary conductor which extends between and joins to opposite butequipotential points in the said first circuit. One way of constructingsuch an arrangement, which we have put into use and found practicallyetlicient, is to havethe first-mentioned circuit in two sectionsconductively separated but inductively united by a repeatinginductioncoil of ordinary construction, the two Windings of the saidcoil and two of the telephones A and B being connected in the twocircuitsections, respectively. In one of the circuitsections the mode ofconnecting its telephone B is immaterial, and it is placed in serieswith the repeating-coil helix; butin the other circuit-section thesecondary winding of the transmitter induction-coil is split or severedcentrally into two equal portions, and the telephone-receiver A, inseries with an impedance coil or device of equal electromagnetic value,(an exactly similar telephone-receiver may, in fact, be employed,) isconnected between the two portions of the said split winding. A pointbetween the said receiver and the impedance and another point at themiddle of the repeating-coil winding are then cquipotential points ofthe same circuit-section, and the auxiliary conductor, including thethird telephone 0, is extended between and unites them. When thisconstruction is adopted, 13 can talk to A but not to O, C can talk to Abut not to B, and A can listen both to B and C but can only talk to B.The invention also com prchen ds the association with such a system ofcircuits of a circuit-changing switch which in one position maintain therelations already described between the three telephones concerned andwhich when placed in a second position reverses or trans poses the saidrelation in such wise that B as sumes in respect to A the formerrelation of C and O the former relation of B, so that A can, as before,hear both, but can now talk to 0 instead of to 13. Thus the transmissionof A is alternative to 13 and C. The circuitchanger, however, can be andpreferably is so devised and constructed as to be capable of assuming athird position, in which A can talk with and hear both B and C and B andO can talk with and hear each other. Moreover, a number of modificationscan be made in the compound-circuit organization without departing fromthe principles of our invention. For instance, the results which, ashereinbefore detailed, can be realized by means of the circuit-changingswitch may also be attained (albeit not alternatively or selectively) bya slightly-changed permanent arrangement of the circuit-conductors.

In the drawings which accompany this specification, Figure 1 is adiagram of a compound-circuit organization exemplifying the principlesof the invention. Fig. 2 is a dia gram of a modified-circuitorganization based on the same principles. Fig. 3 is a diagramillustrating a practical application of the said principles, combinedwith means for transposing the relations of-the several telephonesconcerned; and Fig. 4 is a diagram showing a modification in a detail ofthe construction shown in Fig. 3. Referring in the first place to Fig.1, A, B, and 0 represent three dilterently-placed sets of telephoneapparatus. Risa repeating induction-coil, and I a transmitterinductioncoil. The set A of telephone apparatus is illustrated in detailand shows the arrangement of the transmitter '6, battery Z), and theprimary winding g of the induction-coil I, all in a local circuit 0, thesecondary winding 11 of the said induction-coil centrally divided orsevered into two equal portions "6 and i the receiving-telephone T, andan impedance device D. The latter appliances are joined up in series inthe section L of a conductively-divided circuit L, the receiver T andimpedance D being placed between the two halves of the split secondary.The impedance device may be made of a coil of wire and a suitable ironcore therefor having proportions and an electromagnetic value equal tothat of the receiving instrument T. In fact, a second receiver may beconveniently employed for this purpose. The other section L of theconductively-divided circuit L contains the telephone apparatus 13, andthe two sections contain, respectively, the two windings F and r of therepeating-coil R. The telephone apparatus 0 is connected up in anauxiliary conductor 5, which joins two electrically opposite pointshaving the same potential of the circuit-section L such points beingpoint 10 between the receiverT and impedance device D and point p at thecenter of the repeating-coil winding 0*. \Ve thus have an organizationof two distinct circuits L and E. The circuit L is in twoconductively-divided but inductively-united sections L and L The formercontains in series the telephone or telephone apparatus B and winding 7*of repeating-coil R, uniting them by conductors 2 and 7. The lattersection L contains the other winding 1' of the said repeat-- ing-coil,the portion 2? of the split inductioncoil secondary z',the receiverT,the impedancecoil D, and the remaining portion i of said secondary,these being united in series by conductors 3 and 4. The circuit E, beginning, say,.at point p between receiver T and im pedance D, extends byconductor 5 through the telephone 0 to point p and then by conductors-3and a in parallel (one including the receiver T of telephone A and theother impedance D and each containing one-half of the repeating-coilwinding r and the secondary winding 2') back to the starting-point 1).It is to be stated, however, that the working portion of the circuit isthrough the conductor 3, including the receiver T alone, that portionwhich leads through conductor etand the impedance D being employed forbalancingand neutralizing purposes only. The telephones at B and C maycomprise, of course, both receiving and transmitting instruments, andtheir induction-coil secondaries, which need not be divided, as shown,with telephone A; may be placed in series with the correspondingreceiver, as indicated at B, Fig. 3. The representation of suchtelephones at B and O is therefore to be regarded as conventional orsymbolic simply and not as intended to indicate the presence of areceiver only. The terms telephone and telephonic apparatus as usedherein refer to the telephone instruments of a station con sidered as acomplete apparatus, and where a receiver only is sought to be impliedthe It is maniterm receiver is the one used.

fest from a consideration of the figure that voice-currents originatingin telephone B circulate in section L and by means of the repeating-coilR set up corresponding voicecurrents of identical character in thecircuitsection L These flow through the circuit by way of conductor-s3and 4 and operate the receiver T of telephone apparatus A, reproducingthe words transmitted by B, and if the transmitter 75 of telephone A beoperated the currents developed thereby in the local circuit 0 propagatethemselves in section L by means of the induction-coil I and extendtheir influence to section L by means of the repeating-coil R, thusreproducing the transmitted words in the receiver at B; but as thetelephone 0 is connected between equipotential points of the circuit Lneither Anor B can affect it, and for the same reason the operation of 0cannot effect B, which can be influenced from circuit-section L only bycurrents circulating through the repeating-coil winding 7: from oneterminal thereof to the other. A voice-current originating in virtue ofwords transmitted at O divides at points 19 and p half of it passingbetween said points through receiver T at A and operating the same inresponse to such transmission through the half 2' of the splitcoil-windingz' and one half of winding 7' of the repeating-coil, and theother half passing by way of pointp, impe dance D, and the remaininghalves of coilwindings 2' and r to point 19 and thence over conductor 5to the originating telephone C. The effect of this current, so far astelephone B is concerned, is neutralized by its opposing actions in therepeating-coil,and the receiver .at B is therefore irresponsive; but nosuch neutralizing influence being exercised as regards A the receiver Tof A is perfectly responsive to that portion of the talking-currentwhich passes through it and conversation transmitted at C is received atA.

In Fig. 3 the circuit-section L is the order-circuit, leading to anoperators telephone from anydesired number of other sets of telephoneapparatus ]3,which may be either in the same or diiterent stations. Thetelephones B are shown as being normally disconnected from the circuit,but adapted to be readily brought into connection with it by keys is.They are also shown as comprising the usual receiver and transmitter,with the induction-coil, battery, and local circuit of the latter. Thetelephones A and C are arranged as hereinbefore described, the formerbeing the apparatus of an operator who is required to receive calls froman order-circuit and also supervise connections and send and receivecalls on other circuits, such as substation-lines. Circuit E mayrepresent a substation-line or may be a circuit running to the operatorskeyboard or to keys which can connect with any circuit desired. The saidkeys are represented by the switch \V. As shown in this figure, acircuit-changing switch S, operated by a lever H, fulcrumed at so, is

O can neither talk to nor hear each other.

placed at the junction-point of the circuits of the three telephones A,B, and O, the two latter entering the said junction byasingle pair ofloop conductors having terminal switch springs j 72. and m 11,respectively. Neither circuit is continuous to the repeating-coilwinding 0' or to the equipotential points 19 p but each can bealternatively brought into connection with either by means of two otherpairs of loop-conductors entering diversely from telephone A, one ofwhich loops 6 has its conductors 5 and 6 extending from the said points19 19 while the conductors 7 8 of the otherloop f extend from the twoends of winding 0' of the repeating-coil R. Conductor 5 of loop 6terminates at the circuit-changer S in the fixed outer contacts 8 9 ofthe springs j m, and conductor 6 of the same loop tern1inates in fixedouter contacts 10 and 11. In the same way the conductors 7 S of theother loop f terminate in the inner fixed contacts 12 14: and 13 15,respectively. When the circuit-changer has its handle turned to theleft, the springsj h of circuit L remainin connection with contacts 1213, while the springs of circuit E are thrown outward and into contactwith the points 9 and 11. Under these conditions the organization isexactly that indicated by Fig. 1, wherein A can listen to both B and Oand can talk to B, while B and It the handle of the circuit-changer beturned to the right, we again have the same organization, except that Band C have changed places, B being now connected with the loop 6 and Cwith loop f. The result is thatA can listen to both E and O, as before,but can now speak only to O, B and 0 being still reciprocallyirresponsive, and should the handle of the circuit-changer be placed ina vertical position the spring-terminals of both circuits L and E remainas shown in the figure, one

.pair in contact with points 12 13 and the other with points 1415. Insuch position the organization is a circuit of three branches inderivation, and the operator at A can talk with and hear bothB and O andB and O can talk with and hear one another.

It is not of course essential to our inventionand its operation that therepeating-coil R shall be interposed between the main section L of thecircuit and the other section L thereof. If it be desired to operatethesaid two sections as a continuously-conductive ciredit, the saidrepeating-coil may be dispensed with and an impedance-coilorelectromagnetic resistance R be substituted therefor in the mannerillustrated by Fig. 4. In such a construction the conductor 5 of loop ewill connect with the middle point p of the impedance-coil winding.

Fig. 2 illustrates a modified-circuit organization whereby A is enabledto speak to B and O at all times as well as to hear them. Thetransmitter t in this case has the primary winding (1 of itsinduction-coil placed in inductive relation to the portion 11 only ofthe ICC secondary, this being balanced by a second primaryjoined up inshort circuit with a suitable balancing-resistance r and placed ininductive relation with the portion 2' of the said secondary.

Our invention having now been fully described, we claim-- 1. In atelephone system, the combination of three difierently-placedtelephones; a circuit including two of the said telephones in suchmanner that each may transmit to and receive from the other; and asecond circuit formed in part of a portion of the first including one ofthe said telephones, and in part of an auxiliary conductor joining twoequipotential points of the first circuit, and including the third orremaining telephone, the said third telephone being thereby adapted totransmit to one of the said two telephones of the first circuit but notto the other.

2. The combination in a telephone system, of a telephone-circuit in twoconductively-divided sections; a repeating-coil inductively uniting thesaid sections, and its windings connected one ineach; a telephone in oneof the said sections in series with the repeatingcoil winding thereof;and the split secondary winding of a transmitterinduction-coil, atelephone-receiver, and an impedance device of equal electromagneticvalue in the other of said sections in series with the repeating-coilwinding thereof, the said receiver and impedance being placed betweenthe two halves of the said split secondary; of an auxiliary conductorextended from a point between the said receiver and impedance toacentralpoint of the repeating-coil winding of the same circuit-section; and atelephone connected in the circuit of said auxiliary conductor; substantially as and for the purposes set forth.

3. In a telephone system, the combination of two independenttelephone-circuits, and telephones included therein, the said circuitsextending from theirrespective telephones to a common station; anoperators telephone apparatus at the said station, comprising atransmitter, an induction-coil therefor with a a split secondarywinding, a telephone-receiver, and an impedance device of equalelectromagnetic value, the said receiver and impedance being placed inseries between the two halves of said secondary in a local circuitclosed through one winding of a repeating-coil serving as an auxiliaryimpedance device; a terminal loop for the said local circuit includingand extending from the other windingof said repeating-coil; and a secondterminal loop therefor, the conductors thereof extending respectivelyfrom a point be tween the receiver and its associated impedance device,and from the middle point of the said auxiliary impedance device; and acircuit-changing switch at the junction of the said two independenttelephone-circuits, and the said two terminal loops of the operatorstelephone-circuit, controlling the respective terminal contacts of thesaid circuits and loops, and adapted in one position to maintainconnection between one of the two circuits and the repeating-coil loop,and between the other circuit and the second terminal loop, and inanother position to reverse the order of said connection; substantiallyas set forth.

4. In a telephone system, the combination of two outlying telephones,and independent circuits extending therefrom to the same station; asupervisory telephone apparatus including atransmitter and receiver atthe said station; circuit connections uniting the said transmitter andreceiver to one of the said independent telephone-circuits, and thereceiver only to the other; and a circuit-changing device controllingthe said connections of the supervisory instruments with the saidcircuits respectively, and to reverse or transpose them; substantiallyas set forth.

5. In a telephone system, the combination substantially as hereinbeforedescribed, of three distinct telephone-circuits, converging fromassociated telephone instruments to a common junction-point, two of thesaid circuits enteringthe said junction each bya single pair ofloop-conductors, and the third entering by two pairs of loop-conductors,one of which includes the transmitting and receiving telephones of thecircuit, and the other the receiver only; and a circuit-changing switchat the said junction-point controlling all of the said loop-conductors,and adapted to alternatively connect the two pairs of loopconductors ofthe third circuit with the loopconductors of the two other circuitsrespectively, to reverse or transpose such order of connection, and toconnect the loop which contains both transmitterand receiver of the saidthird circuit with the loops of both of the said other circuits, asdesired.

In testimony whereof I have signed my name to this specification, in thepresence of two subscribing witnesses, this 4th day of February, 1899. c

PEROIVAL G. BURGESS. lVitnesses:

ANDREW H. MoRLAND, JOHN T. JACKSON.

In testimony whereof I have signed my name to this specification, in thepresence of two subscribing witnesses, this 3d day of March, 1899,

HENRY WV. W'ILDER.

W'itnesses:

W. A. GONE, GEO. A. HILL.

